1. Field of the Invention
The invention relates generally to non-metallic protective coverings for the edges of cathode plates used in electrowinning processes. More specifically, the invention pertains to cathode plate edge protector systems formed by secondary and tertiary molding processes, in which fluid plastic is molded around and/or injected into previously molded plastic edge protectors.
2. Description of the Prior Art
The two processing methods used for producing copper are: pyrometallurgy, or smelting, and hydrometallurical leaching. The present invention pertains to the latter method, in which copper bearing ore is pulverized and placed on a leach pad. A weak solution of sulfuric acid is sprayed onto the upper surface of the pulverized ore. The acid solution percolates through the ore, dissolving the acid-soluble copper. The solution is collected in a pond beneath the leach pad.
In the next step, the copper-bearing solution is pumped from the pond to a solvent extraction facility. At this facility, organic chemicals are mixed with the solution, separating the copper into a more concentrated solution. This concentrate is then mixed with sulfuric acid, forming an electrolyte solution.
The final step is the electrowinning process, an electrolytic method used to remove heavy metal ions from concentrated solutions. The copper electrolyte is pumped from the extraction facility into a steel tank at the electrowinning facility. Rows containing alternating cathode and anode plates extend throughout the volume of the tank. The cathode plates are made from stainless steel and the anode plates are made from lead. The plates are vertically suspended, so as to be substantially immersed in the copper electrolyte. The upper ends of the cathodes and the anodes are welded to horizontal hanger bars, which overlay respective electrical buss lines. The buss lines are interconnected to a source of low voltage, high current, DC. The copper ions are reduced through the electolytic process, and deposited as a layers of copper covering the cathode plates. After a week, or so, the cathode plates are removed from the electrolyte and an electroplated copper sheet is stripped from each side of the stainless steel cathode plates.
During this electrowinning process, the copper deposits along the edges of the cathode grow faster and sometimes in a more irregular fashion, that on the planar portions. This causes problems in removal of the copper sheets, as the edge deposited copper is thicker and of varying shape. The prior art teaches the use of non-conductive edge protectors, which extend along the side edges and the bottom edge of the cathode. The edge protectors cover the edges and a small adjacent strip of the planar portion of the cathode. In this way, no copper is deposited onto the edges of the cathode, and a clean line is presented by the inner edge of the edge protector for easy removal of the copper sheet.
Many different designs for these edge protectors have been developed. For example, U.S. Pat. No. 5,690,798, granted to Alexander et al., shows a corner protector for an electrowinning electrode. In this arrangement, a corner protector is located at each corner of the electrode, covering the region where each side edge strip and the bottom edge strip meet in abutting relation. Each corner protector has a vertical channel for receiving the lower end of a side edge strip, a horizontal channel for receiving the end of the bottom edge strip, and a cutout for receiving the corner of the cathode element.
However, the electrolytic process produces heat and expansive forces which compromise the integrity and useful life of prior art edge protectors. Adhesives fail, leaks develop, and deposits eventually form inside the cracks and the cavities of the prior art edge protector systems. When the deposits form in these regions, the edge protectors bulge outwardly and allow further intrusions of the electrolyte. Then, the sheets of deposited copper are difficult to remove, or are damaged during removal, and the cathode plate requires servicing before it can be used again.
Therefore, the need exists for a cathode edge protector system which does not rely upon adhesives, retainer strips, or other mechanical connectors, for attachment to the cathode.
The need exists for a cathode edge protector system incorporating a corner protector molded in situ on the end of one or more edge strips.
The need also exists for a cathode edge protector system which contains no external cracks or defects, or any internal voids, into which electrolyte can seep or intrude.
The need further exists for a cathode plate edge protector system in which edge strips can be preliminarily molded into any desired shape, mounted onto an edge of a cathode plate, and subsequently filled with fluid plastic for structural integration with the cathode plate.
The cathode plate edge protector systems of the present invention are formed by carrying out secondary and tertiary molding processes in conjunction with previously molded or extruded plastic edge protector strips. The first embodiment, a U-shaped edge protector system, is formed by first bevel-cutting the four abutting ends of three edge strips. The strips are then installed into a molding jig to form a U-shaped assembly. The molding jig includes right-angle cavities surrounding the two corners of the assembly. Lastly, fluid plastic is introduced into the cavities, molding plastic corner pieces around the abutting ends of the edge strips, and forming a unitary structure.
The edge protector system is removed from the jig and prepared for installation over the two side edges and the bottom edge of a cathode plate. The cathode plate includes a plurality of plate apertures arranged in spaced relation along its opposing first and second side edges. First and second plastic retainer strips, including a plurality of liked-spaced registration pins on their undersides, are installed along the side edges with the pins fitted into respective apertures.
A second edge protector system is formed by mounting an edge protector strip on the side edge a cathode plate, without a retainer strip. After damming the open ends, a fluid curable into a hardened body is introduced into the contained void between the edge strip and the side edge of the cathode plate. The process is repeated for the opposing edge.
A third edge protector system incorporates aspects of the first system and adds a tertiary molding process. The U-shaped edge protector system of the first system is formed, but it is merely slip-installed onto the cathode plate without using the retainer strips. Then, in a third tertiary molding process, fluid plastic is introduced into the contained void between the edge protector system and the cathode plate, filling the void within the edge protector system and the apertures in the cathode plate. A permanent and integrated structure between the edge protector system and the cathode plate is thereby formed.